Unusually large number of methicillin-resistant Staphylococcus aureus clones in a Portuguese hospital

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) has been endemic in Hospital de Santa Maria, a 1,300-bed teaching hospital in Lisbon, Portugal, since the mid-1980s with a prevalence of 30% in 1993. A total of 54 MRSA and 93 methicillin-susceptible S. aureus (MSSA) isolates recovered during the first 3 months of 1993 were analyzed for the particular mecA polymorphs and Tn554 attachment sites (in the case of MRSA) and for pulsed-field gel electrophoretic patterns. While all MRSA isolates shared a very similar multidrug resistance antibiogram, molecular methods allowed the identification of an unusually large number of genetic backgrounds (24 different pulsed-field gel electrophoresis patterns in 54 isolates) and three different mecA polymorphs among the MRSA strains. Similar large variation in the genetic backgrounds of MSSA was observed. The most frequent mecA polymorph (mecA type I) was found in association with three different Tn554 patterns. Among the MRSA strains of Hospital Santa Maria, we found two clonal types previously described in Portugal: one corresponding to the dominant clone in an MRSA outbreak at the pediatric ward of the Lisbon Hospital Dona Estefânia and another one identical to the Iberian epidemic clone identified in several Portuguese hospitals and in MRSA outbreaks in Barcelona and Madrid. This suggests that MRSA clones of Hospital de Santa Maria may have been a reservoir for staphylococcal strains over the past decade.

Virtually all methicillin-resistant Staphylococcus aureus (MRSA) infections in the largest Portuguese teaching hospital are caused by two internationally spread multiresistant strains: the ‘Iberian’ and the ‘Brazilian’ clones of MRSA

“…As the PFGE pattern did-not change, these genetic events imply no major chromosomal rearrangements and, therefore, one may consider these isolates as still being clonally related to one another. A different type of situation was apparent in some of the minor clones which carried the same Cla1::mecA polymorphs in different genomic (PFGE) backgrounds, suggesting horizontal transfer of the mecA [26,27]. Figure 4 illustrates the temporal shifts in MRSA clonal types observed in the study.…”

Evidence for the geographic spread of a methicillin-resistant Staphylococcus aureus clone between Portugal and Spain

“…The fourth isolate (strain HPV99) was Tn554 negative. The only ClaI-mecA type III strain (HPV15) detected among these 43 isolates showed a new Tn554 pattern, designated ␣, which was recently identified in isolates from two Portuguese hospitals (2,3). Figure 2 shows representatives of the Tn554 patterns found among the clinical MRSA isolates of Hospital Pulido Valente.…”

“…We previously used this technique in combination with other tests to probe the general chromosomal backgrounds of staphylococcal isolates in order to define MRSA clones in molecular epidemiological investigations of MRSA outbreaks at several hospitals in the United States and Europe (2,3,6,7). This molecular fingerprinting technique allowed us to identify from the Hospital Pulido Valente, Lisbon, Portugal, the same MRSA clone that was responsible for recent outbreaks at several hospitals in Spain (6).…”

Analysis of an outbreak of non-phage-typeable methicillin-resistant Staphylococcus aureus by using a randomly amplified polymorphic DNA assay

“…As a result of a routine infection control surveillance, a cluster of MRSA isolates with the same antibiotic susceptibility patterns was noticed on an ICU. Since the antibiogram may be poorly discriminatory (2,22), the MRSA strains were phage typed, which is still a mainstay in the epidemiological analysis of S. aureus infections (7,28). In this case, however, all the MRSA isolates involved in the outbreak were nontypeable by phage typing.…”

“…The discriminatory power of this method depends on the restriction enzymes used (21). PFGE of chromosomal digests with infrequently cutting enzymes has been proposed as the method of choice for typing MRSA (19,25), being a highly reproducible technique with good discriminatory power (7,16), and we applied this technique to our isolates. RAPD analysis and PFGE gave similar results, but PFGE was both more time-consuming and technically demanding.…”